Hinged heart valve prosthesis

ABSTRACT

A heart valve prosthesis has a substantially annular valve body and two leaflets which are disposed in the valve body and, be means of a hinge mechanism, are pivotable between an open position and a closed position. The leaflets are substantially semicircular and evenly curved in two perpendicular directions, one direction being perpendicular to the diameter of the semicircle, so as to bulge outward, as seen from the center of the annulus. The leaflet edges closest to the diameter of the semicircle are so curved that they, when the valve is closed, are applied against one another along their entire length. Further, two projections are provided on the inside of the annulus, entirely within the width thereof, the corner portions of the leaflets being applied against these projections.

The present invention relates to a heart valve prosthesis having anannular valve body and two leaflets which are disposed in said memberand, by means of a hinge mechanism, are pivotable between an openposition and a closed position.

No conventional heart valve prosthesis meets all the requirements madeon such products, which have to function in an extremely reliable mannerand withstand the constant wear caused by the heart beats.

Since heart valve prostheses, hereinafter referred to as heart valves,are implanted in a very sensitive and `cramped` space of the body, it isimperative that they do not damage or get tangled up in the surroundingtissue. Many of today's heart valves suffer from the inconvenience thateither the leaflets proper or projections on the annulus protrude toofar, so that the risk of surrounding tissue interfering with the valvefunction is imminent, especially if the valve is used in the mitralposition. Projections on the annulus may further hinder the surgeon whenimplanting the heart valve.

To emulate the function of the natural heart valve, a prosthesis shouldpreferably have a central flow. It should in addition open and closerapidly and quietly, have an insignificant resistance against flow inthe forward direction, and cause a minimum of turbulence. The artificialheart valve must of course be biocompatible, i.e. acceptable to thebody, and be thrombo-resistant, i.e. not cause or be the residence ofthrombosis. From this point of view, it is essential that all surfacesare well flushed by the blood, so that there are no hidden corners whereclots may form.

U.S. Pat. No. 4,078,268 discloses a heart valve which has an annulus andtwo flat, semicircular leaflets. In one embodiment, the hinge is made upof pins projecting from the leaflets and corresponding holes in theannulus. In another embodiment, both the inside of the annulus and theleaflets are formed with projections which make up the hinges of thevalve. The downstream side of the annulus is provided with triangularprojections on which the leaflets rest when the valve is closed.

U.S. Pat. No. 4,274,437 discloses a heart valve which also has anannulus and two leaflets. These leaflets are sections of a hollow,straight and circular cylinder. The hinge mechanism includes a groove onthe inside of the annulus, as well as two projections fitting in thegroove and provided one on each leaflet. The projections run freely inthe groove, so that the leaflets can rotate in the annulus.

These prior-art valves mainly suffer from the disadvantage that someportions project much too far from the annulus, so that there is aconsiderable risk that they damage, or are themselves hindered by, thesurrounding tissue.

U.S. Pat. No. 4,863,459 discloses another heart valve which has anannulus and two curved semicircular leaflets. This valve has theadvantage of not projecting as far as the other two valves described,but it nevertheless has quite a few drawbacks. Above all, it has nocentral flow and does not close quietly enough.

One object of the invention is to provide a heart valve of this type,which has as low a structural profile as possible, i.e. has a minimum ofelements projecting from the annulus, and which will not damage or gettangled up in the surrounding tissue, either in the open or in theclosed position. This is achieved by a special design of the leaflets.

Another object of the invention is to provide a heart valve whichfunctions also when mounted in a slightly oblique position relative tothe flow direction in the heart. When mounted in this manner, someprior-art heart valves cannot function properly, and as a result one ofthe leaflets stops working, with disastrous consequences for thepatient.

According to the invention, the heart valve prosthesis is characterisedin that the leaflets are substantially semicircular, that the leafletsare evenly curved in two perpendicular directions, one direction beingperpendicular to the diameter of the semicircle, so as to bulge outward,as seen from the center of the annulus, that the leaflet edges closestto the diameter of the semicircle are so curved that they, when thevalve is closed, are applied against one another along their entirelength, and that two projections are provided on the inside of theannulus, entirely within the width thereof, the corner portions of theleaflets being applied against said projections when the valve isclosed.

One advantage of the heart valve according to the invention is the shortpath of movement of the leaflets, which is a result of the curved designof the leaflets and the relatively small angle between the closedposition and the open position. Thus, the short path of movementcontributes to the rapid function and quiet closing of the valve, andalso reduces wear on the hinge mechanism. Quiet operation is verydesirable, because, to some patients, the `clicking` sound of a heartvalve may be deeply worrysome.

Since the valve closes quietly and wear is distributed over a relativelywide area, the heart valve can be made of metal or materials other thanpyrolytic carbon, which is the material most commonly used in today'sheart valves. Pyrolyric carbon has many drawbacks, such as beingexpensive, brittle and invisible on radiographs. A valve made of metal,on the other hand, is much cheaper than a valve made of pyrolytic carbonand can be precision-worked to a much higher degree than a valve ofpyrolytic carbon, which is a ceramic material. Finally, the metalsurface can be coated with a substance (heparin) preventing thrombosis.

Another advantage is that the heart valve according to the invention canbe implanted in all positions owing to its low profile and the fact thatit can be easily turned in the suture ring after implantation.

The preferred embodiment of the invention will now be described in moredetail below, reference being made to the accompanying drawings, inwhich

FIG. 1 is a perspective view as seen from the downstream side of theheart valve according to the invention when closed,

FIG. 2 is a corresponding view of the valve when open,

FIGS. 3 and 4 are perspective views of a leaflet,

FIG. 5 is a side view of a leaflet,

FIG. 6 is a side view of the valve when closed,

FIG. 7 shows the open valve from another angle than FIG. 2,

FIGS. 8 and 9 illustrate parts of the valve as seen from the upstreamside when the valve is open and closed, respectively, and

FIG. 10 is a schematic view of the valve in the aortic and the mitralposition.

As shown in the drawings, the heart valve 1 has an annulus 2 and twoleaflets 3 which are disposed in the annulus and, by means of a hingemechanism 4, 5a, 5b, are pivotable between an open position and a closedposition (see FIGS. 1 and 2). The leaflets 3, which preferably are ofequal size, are essentially semicircular, as appears from FIG. 5, andthe leaflet edge 6 closest to the diameter of the semicircle is curved.As is apparent from FIGS. 3 and 4, the leaflets are evenly curved in twoperpendicular directions, one direction being perpendicular to thediameter of the semicircle. Thus, the leaflets bulge outward, as seenfrom the center of the annulus. Closest to the diameter of thesemicircle, the leaflet edges are so curved that they are appliedagainst one another along their entire length when the valve is closed.Further, the inside of the annulus is formed with two projections 7which are situated entirely within the width of the annulus and againstwhich the corner portions 8 of the leaflets 3 are applied when the valveis closed.

In the direction of its width, the annulus 2 comprises three sections,the mid-section being circular-cylindrical and the other two sectionshaving the shape of truncated cones widening towards the ends of theannulus. Since the annulus of the invention is of essentially the sameconstruction as that disclosed in U.S. Pat. No. 4,863,459, it will notbe described in more detail here.

Owing to the curvature of the leaflets 3 and the leaflet edges 6 as wellas the provision of the projection 7, the corner portions 8 of theleaflets will not be as pointed and project as far as when flat andsemicircular leaflets are used. As illustrated in FIG. 2, the leaflets 3only project a short distance from the annulus 2 on the downstream sidewhen the valve is open, and do not at all project beyond the envelopesurface of an imaginary cylindrical extension of the annulus. On theupstream side, the semicircular leaflet edges 9 only project veryslightly from the annulus.

As illustrated in FIG. 6, the leaflets 3 do not at all project beyondthe annulus 2 on the upstream side when the valve is closed, and onlyproject at the center portion of the annulus on the downstream side.With this construction, there is practically no risk at all that theheart valve may damage, or get tangled up in, the surrounding tissue.

Tests have shown that the leaflet curvature should be more pronounced(greater) in the transversal direction and be in the range of 1:6-1:10,and less pronounced in the longitudinal direction where it should be inthe range of 1:25-1:35. These figures are based on the ratio between, onthe one hand, the distance between a line drawn between the leaflet sideedges and the leaflet upper and lower edges, respectively, and theleaflet crest, and, on the other hand, the distance between the leafletside edges and the leaflet upper and lower edges, respectively, alongsaid line.

As shown in FIGS. 1 and 2 as well as FIGS. 7-9, the hinge mechanism ofthe heart valve according to the invention includes two spaced-apartrecesses 4 formed in the semicircular edge 9 of the leaflets 3, and apair of projections 5a, 5b corresponding to the recesses and provided onthe inside of the annulus. The surface of the leaflet portion movingdownstream when the prosthesis is opened, is approximately twice aslarge as that moving upstream. The projections 5a, 5b--streamlined so asnot to cause too much turbulence--are slightly off-set in relation toone another, in both cases relative to the center plane of the annulusand an imagined vertical line at each hinge. The projection 5a closestto the downstream side of the annulus extends substantially from themiddle of the annulus obliquely towards the projection 7 in thedownstream direction, and constitutes an abutment for the leaflet 3 whenthe valve is open.

The inverse hinge construction, i.e. with recesses in the annulus andprojections on the leaflets, is, however, not outside the scope of theinvention. In any case, it is preferred that the hinge mechanism is sopositioned that about 2/3 of the leaflet surface is situated above animagined axis through the hinge, and about 1/3 thereof is situated belowsaid axis (on the influx side).

As appears most clearly from FIG. 2, the heart valve 1 opens at thecenter, so that the major part of the flow passes between the leaflets3, thereby emulating the function of the natural heart valve.Preferably, the hinges 4, 5a, 5b are so positioned that about 70% of theflow passes between the leaflets 3, i.e. through the central opening.

When the valve is open, the leaflets 3 form an angle of about 75-86°with the annulus 2. The angle is measured between the plane of theannulus and an imagined line between the uppermost and the lowermostpoint of the leaflet. The valve 1 may have different opening angles,e.g. about 80-85°, but preferably has an opening angle of about 85°.When the valve is closed, the leaflet still forms an angle with theannulus, which is about 25-35°.

Owing to the short path of movement between the open and the closedposition (a result of the curved design of the leaflets 3 and therelatively small angle between the open and the closed position) thevalve 1 closes quietly. If the leaflets were to open too widely, i.e.form too large an angle with the annulus 2 in the open position, theblood would have time to accelerate back when the valve closes, andwould then entrain the leaflets which at a high speed would strike theannulus 2. The more gently the leaflet is applied against the annulus 2,the lower is the sound level and the less is the wear on the heartvalve. The leaflet curvature as well as the opening angle of the heartvalve contribute to a gentle return of the leaflets, so that the soundlevel and the wear are maintained at a low level. This makes it possibleto manufacture the outer valve from metal, with all the ensuingadvantages.

Another important parameter in the construction of heart valves isturbulence. It is imperative that the entire heart valve including theannulus 2 and the leaflets have a construction involving a minimum ofturbulence. If the turbulence is too pronounced, the leaflets may cometo `flutter` in the open position, which may increase corpuscledecomposition. To minimize turbulence, the tangent of each leaflet 3 ofthe heart valve 1 halfway between the projections 7 in the open positionof the valve is parallel to the annulus 2 where the distance between theleaflet 3 and the annulus 2 is the smallest. As a result, the tangent isparallel also to the flow direction where the highest velocity of theblood is to be expected.

The projections 7, against which the corner portions 8 of the leafletsare applied when the valve is closed, are also designed for minimalturbulence. As seen from the center of the annulus 2 in FIG. 7, theprojections 7 have essentially the shape of an isosceles triangle, theapex between the equal sides being directed downstream, so that thecorner portions 8 of the leaflets can be applied against the projections7 without any leakage. The equal sides extend all the way to the hingeprojections 5b. Since the heart valve 1 should be as compact aspossible, the projections 7 do not protrude beyond the width of theannulus 2.

In FIGS. 8 and 9, the valve is shown as seen from the upstream side whenopen and closed, respectively. FIG. 9 illustrates that the semicircularleaflet edge 9, when the valve is closed, is applied against the insideof the annulus 2, that the recess 4 in the leaflet 3 is sealinglyapplied against the hinge projection 5b of the annulus 2, and that thecorner portion 8 of the leaflet is applied against the projection 7 ofthe annulus 2. When the valve is open, as shown in FIG. 8, the leafletcan move slightly in the flow direction, the hinge mechanism having aplay to promote effective flushing thereof.

The heart valve according to the invention is suitably implanted in theaortic as well as the mitral position, and may also be used in thepulmonary and the tricuspid position, if required. The aortic position11 and the mitral position 10 are shown in FIG. 10. It should beobserved that when the valve is used in the mitral position, theleaflets on the downstream side move in the same direction as the valveleaflets of the natural mitral valve. Thus, the valve prosthesisaccording to the invention can be used even if parts of or the entiremitral-valve assembly is retained, which results in an improved heartfunction after the operation. The blood flow is more rapid in the aorticposition 11 than in the mitral position 10, so that heart valves ofdifferent sizes and opening angles may have to be implanted in the twopositions. However, the heart valve according to the invention can beused in all of the positions mentioned above.

For anatomical reasons, it may at times be necessary to implant theheart valve 1 in a slightly oblique position relative to the blood flow.With the heart valve according to the invention, this is easily done,since the curvature of the leaflets enables the heart valve according tothe invention to function also if mounted in such an oblique position.

To enable implantation in the heart, the heart valves mounted in aso-called suture ring. The heart valve 1 according to the invention canbe turned in the suture ring 2 also after the implantation. Further, theprojections 7 form two parallel surfaces which are perpendicular to theplane of the annulus 2 and which can be engaged by a tool for turningthe heart valve in the suture ring. This can be done because of thecompact design of the heart valve, leaving no projections which maydamage the surrounding tissue.

I claim:
 1. A heart valve prosthesis, comprising:an annular valvemember; and two substantially semicircular leaflets supported in saidannular valve member by a hinge mechanism so as to be pivotable betweenan open position and closed position, each leaflet being evenly curvedin two orthogonal directions, one of which is perpendicular to adiameter of the leaflet, such that said leaflets bulge in an outwarddirection relative to a center of said annular valve member and abut oneanother along an entire length of respective diametral edges thereofwhen in a closed position, said hinge mechanism having hinge membersincluding a pair of spaced-apart recesses and a cooperating pair ofhinge projections for each leaflet, said pair of projections beingdisposed on one of an inside of said annular valve member and asemicircular edge of the leaflet, and said pair of recesses beingdisposed on the other of said inside of said annular valve member andsaid semicircular edge of the leaflet, said hinge members beingpositioned such that said leaflets open in said outward direction andallow at least 70% of a bloodflow through said annular valve member topass therebetween; and a pair of substantially isosceles-triangle-shapedsealing projections disposed entirely within a width of said annularvalve member so as to sealingly abut corner portions of said leafletsnear opposite ends of said diametral edges of said leaflets when saidleaflets are in said closed position, with a respective apex betweenequal sides of each sealing projection being directed in said outwarddirection and said equal sides extending substantially to two of saidhinge members formed on said inside of said annular valve member.
 2. Aheart valve prosthesis according to claim 1, wherein a respective lineconnecting points of extremity of each leaflet along an axis of saidannular valve member when said leaflets are in said open position formsan angle of about 75-86° with respect to a plane of said annular valvemember.
 3. A heart valve prosthesis according to claim 1, wherein saidannular valve member has three widthwise sections including acylindrical mid-section and two oppositely outwardly wideningtruncated-cone-shaped end sections.
 4. A heart valve prosthesisaccording to claim 3, wherein a tangent of each leaflet at a pointmid-way between said sealing projections and closest to said annularvalve member when said leaflets are in said open position is parallel toan axis of said annular valve member.
 5. A heart valve prosthesisaccording to claim 1, wherein curvature of each leaflet is greatertransversely of the leaflet than longitudinally of the leaflet.
 6. Aheart valve prosthesis according to claim 1, wherein said hinge membersare positioned such that 2/3 of a surface of each leaflet is situated toone side of a hinge axis of the leaflet towards said outward direction,and 1/3 thereof is situated to an opposite side of the hinge axis towarda direction opposite to said outward direction.